1. Field of the Invention
The present invention relates to integrated circuit laser diode drivers; and, in particular, the present invention relates to integrated circuit laser diode drivers suitable for use in high frequency applications, such as fiber optics.
2. Discussion of the Related Art
Laser diodes are widely used in fiber optic data and telecommunication communication applications, such as Fiber Channel, FDDI or SONET. For these applications, laser diodes operate at switching frequencies as high as 2.5 Gb/s. Laser diode drivers for driving such laser diodes are available in integrated circuit form. However, such integrated circuit laser diode drivers require both high overhead supply power and numerous external components.
FIG. 1 shows a laser diode 101 driven by an integrated circuit laser diode driver 150. As shown in FIG. 1, a laser diode 101 is driven by output terminals 112 and 113 of integrated circuit laser diode driver 150. Terminal 112 is the output terminal of a differential amplifier 103 for providing a DC prebiasing current for laser diode 101. Prebiasing allows laser diode 101 to operate close to its threshold current level. Prebiasing minimizes the turn-on delay of laser diode 101 during operation. In one implementation of circuit 100, the DC prebiasing current is approximately 20-80 ma. The prebiasing DC current level in terminal 112 is controlled by a feedback path including photodiode 102 and amplifier 104. The current in photodiode 102 is amplified by amplifier 104 and provided to the inverting input terminal 118 of differential amplifier 103. The non-inverting input terminal of differential amplifier 103 receives at input terminal 119 a relatively constant current from reference current source 111.
A signal to be transmitted by laser diode 101 is received by integrated circuit laser diode driver 150 as a differential signal in terminals 114 and 115. Buffer stage 105 amplifies the differential signal received by terminals 114 and 115 and provides at terminals 116 and 117 a differential signal, which is modulated by differential amplifier 140. Differential amplifier 140 is formed by transistors 107 and 108, and current source 106. Differential amplifier 140 provides at node 120 a modulated unipolar AC signal, which is injected into laser diode 101. External capacitor 110 and external inductor 109 are provided respectively to pass and block the AC signal.
As evident from FIG. 1, the amplitude of the modulated AC current signal injected into laser diode 101 also determines the requisite current in current source 106. Since the current in current source 106 is a static current, the larger this current is, the larger the power dissipation in integrated circuit laser diode driver 150. In one typical configuration of circuit 100, this current is between 5 to 40 ma. An example of such a laser diode driver is the IDA-07318 integrated circuit available from Hewlett-Packard Company.